AQA A-LEVEL CHEMISTRY PERIOD 3 Questions and Answers

AQA A-LEVEL CHEMISTRY PERIOD 3 Questions and Answers reaction of sodium with water- observation Floats, fizzes and moves on the surface of the water, molten. melts into a ball and disappears pH of sodium with water alkali, 12-14 sodium oxide formula Na2O What is the structure bonding in NaO ionic lattice, ionic bonding between Na+ ions an O2- ions Why is the melting point of sodium oxide high? ionic lattice with strong electrostatic forces of attraction between ions (Na and O) so a lot of energy is required to break it formation of sodium oxide equation 4Na+O2-- 2Na2O formation of sodium oxide- observation, burning Na in air burns vigorously in air with yellow flame and white solid formed Describe sodium as an alkali metal. needs to be stored in oil to prevent it from reacting with air. can be cut with a knife, exposing a shiny surface which tarnishes quickly - forming layer of Na2O. sodium oxide and water equation Na2O+H2O-- 2NaOH sodium oxide and HCL equation Na2O+2HCL-- 2NaCl+H2O sodium oxide and sulfuric acid equation Na2O+H2SO4-- Na2SO4+H2O sodium oxide and water reaction description sodium oxide dissolves in water and the oxide ion acts as a base and accepts H+ from the water or acid how quickly does magnesium react with water? magnesium reacts very slowly with water forming a solution of pH 9-10. But vigorously with water vapour above 100c (steam)... in absence of air. magnesium and water equation Mg+2H2O(l)-- Mg(OH)2+H2 magnesium and water vapour equation Mg+H2O(g)-- MgO+H2 What is the structure bonding in magnesium oxide? ionic lattice structure, ionic bonds between positive Mg ions and negative O ions. why is the melting point of magnesium oxide high? due to the strong electrostatic forces of attraction between oppositely charged ions (Mg and O) in the ionic lattice, which require a large amount of energy to break why is the melting point of magnesium oxide high than sodium oxide Mg2+ ions is smaller and has a higher 2+ charge than the Na+ ion. the electrostatic forces of attraction between the Mg2+ ions and the O2- ions are higher than between the Na+ and O2- ions magnesium burning in oxygen observation vigorously, bright white light and a white solid forms magnesium oxide and water equation MgO+H2O-- MgO(OH)2 magnesium and oxygen equation (burning) 2Mg+O2-- 2MgO pH of solution of magnesium oxide slightly alkali, around pH9-10 magnesium oxide and HCL equation MgO+2HCL-- MgCl2+H20 magnesium oxide and H2SO4 MgO(s) + H2SO4(aq) -- MgSO4(aq) + H2O(l) Al reaction with oxygen 2Al + 3/2O2 -- Al2O3 Burning Al observations Slow, n/a flame colour, produces Al2O3 Describe reaction of Al2O3 in water Partially ionic an partially covalently bonded, insoluble in water. Why is Al2O3 amphoteric? use equations Act as an acid or base, forming salts when reacting with an acid or base. Al2O3(s) + 3H2SO4(aq) -- Al2(SO4)3(aq) + 3H2O Al2O3(s) + 2NaOH(aq) + 3H2O -- 2NaAl(OH)4(aq) Reaction of Si with oxygen Si + O2 -- SiO2 Reaction of Si in air/burning? observations Slow, n/a colour, produces SiO2 The Reaction of SiO2 with Water Giant covalent structure means insoluble in water. Reaction of SiO2 with acid/base. React with bases to form salts so classified as acidic. SiO2(s) + 2NaOH(aq) -- Na2SiO3(aq) + H2O(l) Reaction of P with oxygen P4(s) + 5O2 -- P4O10(s) Burning P in air observations Spontaneously combusts, brilliant white flame, produces P4O10 Reaction of phosphorous oxide with water. Simple covalent oxide forms acidic solutions. P4O10(s) + 6H2O -- 4H3PO4(aq) Phosphoric(V) acid produces. H3PO4 -- 3H+(aq) + PO4(3-)(aq), dissociate to conjugate base Strong acid, pH = 1 Phosphorous oxide acting as acid or base? Acidic so neutralise bases. P4O10(s) + 12NaOH -- 4Na3PO4(aq) + 6H2O(l) Reaction of S with oxygen S(s) + O2 -- SO2 Can form SO3 Burning S in air observations Burns steadily, blue colour flame, produces SO2 Reactions of SO2 in water SO2 + H2O -- H2SO3(aq) Sulfurous acid (sulfuric(IV) acid). Simple covalent oxides form acidic solution of pH = 1. Dissociates: H2SO3 -- 2H+ + SO3(2-) Reactions of SO3 in water SO3 + H2O -- H2SO4(aq) Sulphuric(VI) acid. Simple covalent oxide forms strongly acidic solution of pH = 1. Dissociates: H2SO4 -- 2H+ + SO4(2-)